Field of the Invention
The invention relates to a muffler and an associated assembly having a metallic catalyst carrier body or support structure for exhaust gas cleaning or emission control, in particular of small engines. The invention also relates to a method for producing such an assembly.
Catalyst carrier bodies for exhaust gas cleaning which have retaining elements are known. Published French Patent Application 2 444 793 describes a carrier body in which metallic clamping bands are used for positionally fixing the catalyst carrier body assembly. However, the clamping bands are not intended for fastening to an exhaust pipe casing. Instead, as far as the exhaust pipe casing is concerned, portions have to be circumferentially formed onto the periphery of the catalyst carrier body in an additional operation. A special additional production apparatus is required for that purpose, in order to ensure that the carrier body is fastened in the exhaust pipe casing in a sealing manner.
German Patent DE 38 29 668 C2 describes an exhaust muffler for two-stroke engines with a mounting for a catalyst carrier body. In that case the mounting forms an exhaust space through the use of two profiled plates. On one hand, the catalyst carrier body is provided in a known way with a tubular jacket on which the plates are correspondingly supported and fastened. The plates are fastened on the catalyst carrier body provided with the tubular casing, in such a way that the structure as a whole points away from the supporting region but does not penetrate the latter. On the other hand, the profiled plates also include a part of the exhaust tail pipe, with the result that the production of such complicatedly profiled plates is cost-intensive and, in particular for catalytic converters of small engines, does not appear to be particularly suitable.
U.S. Pat. No. 4,795,615 describes a catalyst carrier body in which jacket clamping strips are provided for positional fixing in the exhaust pipe system. Although the jacket clamping strips ensure a positional fixing in the exhaust pipe casing, the catalyst carrier body must have further devices to allow it to be kept in a dimensionally stable state during transportation until it is installed into the exhaust pipe casing. European Patent 0 470 113 B1 describes a catalyst carrier body which has a tubular jacket to allow it to be transported in a dimensionally stable state to a location where it is installed into an exhaust pipe system. The tubular jacket has a circumferential bead on which a retaining plate can be fastened. That retaining plate serves for further fastening in the exhaust pipe casing of a unit including the retaining plate, the tubular jacket and the catalyst carrier body.
Furthermore, German Published, Non-Prosecuted Patent Application 27 46 475 describes a catalyst carrier body in which a tensioning band is placed around a carrier body. Overlapping ends of the band are fastened on an inner periphery of the exhaust pipe casing. Although such a tensioning band serves the possibility of allowing the carrier bodies to be transported separately to the place where they are installed, fastening in the exhaust pipe casing in a mechanically stable manner, including with respect to vibration, is difficult to accomplish in that way. That is because the tensioning band is intended to take up thermal expansions and therefore cannot be connected entirely at its periphery to the exhaust pipe casing.
It is accordingly an object of the invention to provide an assembly which has a catalyst carrier body and a retaining element, can be transported in a dimensionally stable state, does not require a tubular casing, can be produced at low cost and can be easily adapted and fitted into an exhaust pipe casing, a corresponding muffler for installation of such assemblies and a method for producing an assembly, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, an assembly for cleaning exhaust gas or emission control, in particular of a small engine, comprising a metallic catalyst carrier body without a tubular jacket for installation in an exhaust pipe casing, the catalyst carrier body having a longitudinal axis, an interior with a plurality of flow paths and a jacket surface; and at least one substantially plate-shaped retaining element to be fastened in the exhaust pipe casing, the retaining element having an opening formed therein for receiving and securing the catalyst carrier body, the retaining element having a protrusion, such as a flanging or a collar, surrounding only part of the jacket surface of the catalyst carrier body, in particular enclosing substantially the entire periphery, the retaining element fastened directly on the catalyst carrier body, and the retaining element holding the catalyst carrier body together in a dimensionally stable state and/or substantially supporting the catalyst carrier body on its own.
In accordance with another feature of the invention, the retaining element can be connected to the exhaust pipe or muffler casing, which has an inflow chamber for the exhaust-gas flow to be treated and an outflow chamber for the treated exhaust-gas flow, with the two chambers interconnected through the catalyst carrier body, in such a way that a first part of the carrier body faces the inflow chamber and a second part of the carrier body faces the outflow chamber, which is separated from the inflow chamber in a sealing manner. Preferably, the first and second parts of the carrier body are made to have approximately the same length. However, corresponding conditions for installing the catalyst carrier body into the exhaust pipe casing, particularly if the latter is a muffler casing, may necessitate distributions of length other than this. Since it is fastened directly on the carrier body, the retaining element serves for directly ensuring the dimensional stability of the catalyst carrier body once it has been produced. The form which is customary in the case of metallic honeycomb structures, obtained by laminating, winding or intertwining at least partially structured layers of sheet metal to form a honeycomb assembly, would not be dimensionally stabilized adequately if precautions were not taken to prevent the assembly from coming apart again. If a retaining element is pushed over the assembly once it has been produced, its dimensional stability is consequently ensured, with the result that the catalyst carrier body can be transported with the retaining element provided directly on it, without dimensional stability having to be accomplished through the use of a tubular jacket or auxiliary devices.
The retaining element is further constructed in such a way that it corresponds to the inner form of the exhaust pipe casing and thus also serves for direct fastening within the exhaust pipe casing. This fastening is configured in such a way that the exhaust pipe casing is reliably subdivided, in an essentially sealing manner, into an inflow chamber, into which the exhaust-gas flow to be treated enters, and an outflow chamber, into which the treated exhaust-gas flow enters from the catalyst carrier body. This provides a very low-cost component which, along with greater flexibility and adaptability to the widest variety of geometrical configurations of the exhaust pipe casing, additionally has the decisive advantage that the widest variety of types of catalyst carrier bodies can be used. For instance, radial catalysts, axial catalysts, i.e. honeycomb structures which can be flowed through essentially radially or axially, as well as so-called diagonal catalysts, can be readily used. Diagonal catalysts are to be understood as meaning those which have in the interior of the catalyst carrier body flow paths that have both a radial directional component and an axial directional component.
In accordance with a further feature of the invention, the retaining elements are constructed in the form of plates. In a preferred embodiment, the retaining element is configured as an essentially planar plate. The use of a planar plate is particularly advantageous, since a planar plate can be easily produced with an opening adapted to the form of the catalyst carrier body and can also be easily adapted to the inner form of the exhaust pipe casing.
In accordance with an added feature of the invention, the retaining element has an approximately elliptical opening for obliquely configuring a cross-sectionally round catalyst carrier body therein. A greater region of the periphery of the actual catalyst carrier body is retained in a dimensionally stable state because the carrier body is disposed obliquely in the retaining element. Furthermore, adaptation to given space conditions is easily possible.
In accordance with an additional feature of the invention, the opening of the retaining element has a collar at its rim. The collar may be produced by production processes which are known per se, such as drawing forming processes for example, when incorporating the opening. One of the purposes served by the collar is for better fastening and for ensuring better dimensional stability of the actual catalyst carrier body without a tubular jacket. Welding of the collar onto the catalyst carrier body is easier than welding into a collarless opening.
In accordance with yet another feature of the invention, in the case of elliptical openings, the rims on the narrow sides are flanged, with the result that an obliquely inserted catalyst carrier body bears on both sides against the flangings.
In accordance with yet a further feature of the invention, the provision of a retaining element allows the preferred use of a structure of an axial type, with a honeycomb structure, as the catalyst carrier body or, in a similarly preferred way, the use of a structure of a radial type, likewise with a honeycomb structure.
With the objects of the invention in view there is also provided a method for producing an assembly for cleaning exhaust gas, which comprises producing a catalyst carrier body with a longitudinal axis, an interior having a plurality of flow paths and an outer surface, but without a tubular jacket, in a production device, for installation of the catalyst carrier body into an exhaust pipe casing; producing at least one approximately plate-shaped retaining element having an opening formed therein and a protrusion in the vicinity of the opening in the form of a flanging or a collar; passing the completed catalyst carrier body directly from the production device into the opening with the protrusion surrounding only part of the outer surface of the catalyst carrier body; and fastening the protrusion directly on the outer surface of the catalyst carrier body, preferably by welding or by a form-lockingly connection, with the retaining element holding the catalyst carrier body together in a dimensionally stable state and/or substantially supporting the catalyst carrier body on its own. The carrier body is introduced directly from the production device into the opening provided in the retaining element after winding or laminating or intertwining at least partially structured layers of sheet metal.
The opening is preferably constructed in such a way that the longitudinal axis of the catalyst carrier body is inclined with respect to a direction substantially perpendicular to a plane identifying the extent of the retaining element. The retaining element is fastened directly to the outer surface of the catalyst carrier body in a sealing manner all the way around the periphery in the region of the opening. In other words, the actual catalyst carrier body has no tubular jacket. The catalyst carrier body which is produced by this method and provided with the retaining element can consequently be transported separately. The catalyst carrier body can be fitted into any desired forms of exhaust pipe casing according to the outer shaping of the retaining element, and can be fastened on or in the latter in such a way that the retaining element represents a baffle plate and subdivides the exhaust pipe casing into an inflow chamber for the exhaust gas to be treated and an outflow chamber for the treated exhaust gas.
In accordance with another mode of the invention, the catalyst carrier body is only wound, laminated or intertwined, in particular from layers of sheet metal already coated with ceramic and/or catalytically active material, at least in subregions, without the points of contact of a plurality of layers lying one on top of the other being brazed. Depending on the type of fastening of the retaining element to the layers of sheet metal, it may be necessary not to provide any coating at the connecting points, or to remove it again there. It may also be advisable to provide only some of the layers of sheet metal with catalytically active material, in order to keep the thermal loading caused by the exothermal conversion of exhaust gas constituents within limits.
In accordance with a further mode of the invention, the catalyst carrier body is produced from layers of sheet metal formed of expanded metal.
It is further preferred to wind or stack the catalyst carrier body from a foil assembly, with the result that the foil assembly can be brought into any desired form permitting the actual catalyst carrier body to be fitted into existing exhaust pipe casings according to the given design conditions. The catalyst carrier body preferably includes a foil with a corrugated structure obtained by arbitrary introduction into a space with inner dimensions and inner shapings which corresponds to the outer form of the actual catalyst carrier body. The foil having such a corrugated structure is, as it were, xe2x80x9cfiredxe2x80x9d into a corresponding entry opening into such a space, with the result that a chaotically laminated catalyst carrier body is produced. The retaining element is preferably fitted as a dividing wall into an exhaust pipe casing and adhesively bonded there to the casing wall in a sealing manner, or is welded to the latter or curled with its border into a circumferential edge of the casing, with the result that two chambers interconnected through the catalyst carrier body are formed. In particular, a muffler casing with an obliquely fitted catalyst carrier body can be formed in this way.
With the objects of the invention in view, there is additionally provided a muffler for an exhaust system of a small engine, comprising a metallic catalyst carrier body with a jacket surface but without a tubular jacket; a muffler casing having an inflow chamber and an outflow chamber; and a dividing wall mutually separating the inflow and outflow chambers, the dividing wall constructed as an approximately plate-shaped retaining element for the catalyst carrier body, the dividing wall having an opening formed therein obliquely receiving the catalyst carrier body, the dividing wall having a protrusion, such as a flanging or a collar, at the opening surrounding only part of the jacket surface of the catalyst carrier body, and the protrusion fastened directly on the catalyst carrier body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a muffler and an associated assembly having a catalyst carrier body and a retaining element and a method for producing the assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.